Photoelectric proximity detector and switch

A detector for sensing proximity of objects within a sensing region, comprising,

• light emitter means for emitting light in a given general direction in the sensing region,
• frequency modulation means for modulating the light emitter means to produce a pulsed output at a selected frequency,
• detector means for receiving reflected light emitted by the light emitter means and reflected off an object positioned in the sensing region, and for producing an electrical signal having a frequency component matched to said selected frequency,
• signal processing means receiving the electrical signal from the detector means, for producing a processed signal which is representative of the amplitude of said frequency component of the electrical signal, and
• compensating means for subtracting from the amplitude of the processed signal a compensating value representing the magnitude of expected extraneous light received by the detector means substantially at said selected frequency, and for producing a compensated signal,
• whereby the compensated signal may be used to determine whether an object is present in the sensing region, by applying a threshold, or the amplitude of the compensated signal may be used to determine proximity of the object to the detector means.

A touch detector for activating circuitry behind a transparent divider such as a glass window positioned to make a division between an inside space and an outside space, so as to let a user select desired information or other visual materials to be displayed from behind the transparent divider, comprising,

• a touch area indicator adjacent to the inside surface of the transparent divider, indicating to a user a touch area to be touched for making selections,
• light emitter means adjacent to the touch area indicator at the inside of the transparent divider, for emitting light outwardly through the transparent divider, toward the touch area,
• frequency modulation means for modulating the light emitter means to produce a pulsed output at a selected frequency,
• light detector means adjacent to the light emitter means at the inside of the transparent divider, oriented toward the outside, for receiving reflected light emitted by the light emitter means and reflected off a finger when present in the touch area at the outside of the transparent divider, and for producing an electrical signal having a frequency component the same as said selected frequency when a finger is present at the touch area,
• signal processing means receiving the electrical signal from the light detector means, for producing a processed signal which is representative of the amplitude of said frequency component of the electrical signals when present,
• compensating means for subtracting from the amplitude of the processed signal a value representing the magnitude of expected extraneous light received by the detector means substantially at said selected frequency, said extraneous light comprising a substantially constant level of emitted light reflection from surfaces of the transparent divider, as a constant background level of signal at the selected frequency, and for producing a compensated signal, and
• threshold comparator means for further processing the compensated signal to apply a preselected threshold and to determine whether the compensated signal is sufficient to indicate the presence at the touch area of a finger reflecting the emitted light to the detector, and for producing a switching signal output when it is detected that a finger is present.

A method for sensing touch by a user at a touch area at the outside of a transparent divider, without breaching the integrity of the transparent divider, comprising,

• providing a touch detector apparatus adjacent to the inside surface of the transparent divider,
• emitting light, modulated at a selected frequency to produce a pulsed beam, from the touch detector apparatus through the transparent divider, toward the touch area,
• sensing modulated light thus emitted and reflected back from the touch area, using a photodetector means of the touch detector apparatus,
• producing an electrical signal from the photodetector means, having a frequency component the same as the selected frequency at which the emitted light is modulated,
• processing the electrical signal from the photodetector means to produce a processed signal which is representative of the amplitude of the frequency component of the electrical signal, without modulation,
• subtracting from the amplitude of the processed signal a value representing the magnitude of expected extraneous steady-state light received by the photodetector means substantially at the selected frequency, thereby producing a compensated signal, and
• making a comparison of the compensated signal with a reference value representative of a selected threshold indicative of the presence of a finger at the touch area, and producing a binary state output to indicate a touch when appropriate.

A method for sensing proximity of an object at a sensing region at the outside of a transparent divider, without breaching the integrity of the transparent divider, comprising,

• providing a detector apparatus adjacent to the inside surface of the transparent divider,
• emitting radiation, modulated at a selected frequency to produce a pulsed beam, from the detector apparatus through the transparent divider, toward the sensing region,
• sensing modulated radiation thus emitted and reflected back from the sensing region, using a detector means of the detector apparatus,
• producing an electrical signal from the detector means, having a frequency component the same as the selected frequency at which the emitted radiation is modulated,
• processing the electrical signal from the detector means to produce a processed signal which is representative of the amplitude of the frequency component of the electrical signal, without modulation, and
• subtracting from the amplitude of the processed signal a value representing the magnitude of expected extraneous steady-state radiation received by the detector means substantially at the selected frequency, thereby producing a compensated signal having an amplitude representing proximity of an object present in the sensing region,
• whereby the compensated signal may be compared with a reference value representative of a selected threshold indicative of the presence of an object in the sensing region so as to produce a binary state output to indicate the presence of an object when appropriate, or the amplitude of the compensated signal may be used to measure proximity of such an object in the sensing region.